What does "midshipman" mean?

Midshipman: (Zoöl.) An American marine fish of the genus Porichthys, allied to the toadfish. Cadet midshipman, formerly a title distinguishing a cadet line officer from a cadet engineer at the U. S. Naval Academy. See under Cadet. -- Cadet midshipman, formerly, a naval cadet who had served his time, passed his examinations, and was awaiting promotion; -- now called, in the United States, midshipman; in England, sublieutenant.